JPH0933378A - Method for inspecting pipe by electromagnetic wave - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the detection error due to the stationary electromagnetic field distribution within a pipe, in an inspection method for detecting a leakage position such as corroded hole generated in a pipe such as gas pipe by use of electromagnetic waves. SOLUTION: In the method of inspecting a leakage position 36 of a pipe 14 to be inspected by exciting an electromagnetic wave to the pipe 14 by a transmitting device 11, propagating it in the pipe, and receiving the leaked electromagnetic wave by a receiving device 12, the frequency of the excited electromagnetic wave is changed with the lapse of time. The frequency can be continuously changed by sweeping, or stepwise. Since no stational electromagnetic field distribution is formed in the pipe, the leakage of electromagnetic wave from a leakage position can be surely judged, thereby, the detection of the leakage position can be ensured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection method for detecting leak points such as corrosion holes formed in a gas pipe by using electromagnetic waves.

[0002]

2. Description of the Related Art As one of methods for detecting a leaked portion such as a corrosion hole formed in a gas pipe, a detection method using electromagnetic waves has been proposed. In this method, an electromagnetic wave of a certain frequency is excited in a metal gas pipe, propagated in the same manner as a circular waveguide, and an electromagnetic wave leaking from the leaking part is received to detect the leaking part. Is. FIG. 6 schematically shows a conventional configuration to which this method is applied. Reference numeral 1 is a transmitter, 2 is an excitation unit, 3 is a coaxial cable,
The exciter 2 is attached by cutting one end of the gas pipe 4.
It is configured as a coaxial-circular waveguide converter with a probe 5 protruding therein. Reference numeral 6 is an antenna, and 7 is a receiving device. In the above configuration, the excitation unit 2 is provided on the transmitter 1 side.
In this state, the worker on the receiving device 7 side searches the electromagnetic wave leaking from the leaking point 8 while moving the antenna 6 while continuously exciting the electromagnetic wave.

[0003]

Depending on the state of the gas pipe as an electromagnetic wave transmission line and the frequency of excitation, an electromagnetic field distribution in the pipe may be formed so that the electromagnetic wave is less likely to leak from the leak point. In such a case, it becomes difficult to detect the leakage point. However, it is not possible to preset a frequency suitable for detection so that such an electromagnetic field distribution is not formed. The present invention aims to solve such problems.

[0004]

In order to solve the above-mentioned problems, in the present invention, an electromagnetic wave is excited by a transmitting device into a pipe to be inspected to propagate in the pipe, and a leaking electromagnetic wave is received by a receiving device. In the method of inspecting a leaked part of a pipe, it is proposed that the frequency of the electromagnetic wave to be excited is changed with time.

The present invention proposes that the frequency of the electromagnetic wave is continuously changed by sweeping or is changed stepwise in the above-mentioned configuration.

[0006]

When the frequency of the electromagnetic wave excited in the pipe is changed with time, even if an electromagnetic field distribution that is difficult to leak from a leak point at a certain frequency occurs at a certain time,
The electromagnetic field distribution changes at different frequencies, and the electromagnetic waves leak from the leaking point, so that the leaking point can be detected.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 schematically shows the overall construction of an embodiment in which the method of the present invention is applied to the detection of a leak location in a gas pipe.
Reference numeral 11 is a transmitting device, 12 is an exciting unit, and 13 is a coaxial cable that connects the transmitting device and the exciting unit 12. In this embodiment, the exciter 12 does not cut the gas pipe 14, but the lid 17 of the opening 16 on the side of the tee 15 that is installed in advance.
The probe 18 and the loop (not shown) are projected into the tee 15 by being attached to the. An example of the specific configuration of the excitation unit 12 will be described later with reference to FIG.

The transmitter 11 includes an oscillator, an amplifier, etc.
In addition to the basic constituent elements necessary for exciting the electromagnetic wave, it constitutes means for changing the frequency of the exciting electromagnetic wave with time. 2 to 4 schematically show examples of changes in frequency with time. First, in FIGS. 2 and 3, the frequency is continuously changed by sweeping in a certain range. In FIG. 2, the frequencies are low → high, high → low, low → high, ...
..., the frequency changes from low to high and low to low in Fig. 3.
High, low → high, and so on. As a means for obtaining such a change in frequency over time, the transmitter 11
The oscillator may be composed of a swept oscillator. Next, FIG. 4 shows a stepwise change of a plurality of frequencies.
As a means for obtaining such a frequency change with time, the oscillator of the transmitter 11 may be configured by a programmable oscillator capable of setting a plurality of oscillation frequencies. Code 2
1 is a receiving device, 22 is a receiving device 21 and a coaxial cable 23
It is the antenna connected by. The receiver 21 has a detector,
An amplifier, a signal processing device, a reception level display device, and the like are configured to be able to receive electromagnetic waves in the above frequency range.

FIG. 5 specifically shows an embodiment of the exciting section 12. The same components as those shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted. In FIG. 5, reference numeral 2
Reference numeral 4 is a support, and 25 is a lock nut, which are connected by a screw portion 26. Lock nut 2
The screw portion 26a of 5 is a mounting hole 27 formed in the center of the lid 17.
From the inside, and by screwing and tightening with the screw portion 26b of the support body 24 arranged inside, the periphery of the mounting hole 27 of the lid 17 is held by the collar portion 28 of the lock nut 25 and the support body 24. It is supposed to be fixed.
Prior to such screwing, the tip of the coaxial cable 13 is inserted into the lock nut 25, the center lead 29 is projected, and the braid of the shield wire 30 is expanded along the clamp 31. A washer 32 and a gasket 33 are provided on the tip side of the above, and the expanded shield wire 30 is pressed against the inner wall of the support body 24 by the above-mentioned tightening to be in a mounted state. On the other hand, a linear probe 18 is joined to the tip side of the center lead 29, and the probe 18 is supported by an insulator 34 at the center positions of the supports 35a and 35b. In such a configuration, the lid 1
The threaded portion 35a of No. 7 can be closed by screwing the threaded portion 35a of the tee 15 into the threaded portion 35b of the opening 16 on the side of the tee 15 and tightening the probe.
Located inside.

In the above structure, when the transmitter 11 supplies the electromagnetic wave to the exciter 12 by the coaxial cable 13, the electromagnetic wave in the mode corresponding to the electric field generated by the probe 18 is excited in the tee 15, and the tee 15 causes the gas pipe 14 to flow.
Propagate to. In this way, the gas pipe 14 can propagate electromagnetic waves in the same mode as the circular waveguide. In the case of the figure, an electromagnetic field of TM ₀₁ mode is formed and propagates in the gas pipe 14.

The gas pipe 14 has a leakage point 2 such as a corrosion hole.
6 exists, leakage of electromagnetic waves occurs at the leakage point 26 due to a magnetic field component in the pipe wall direction and an electric field component in a direction perpendicular to the pipe wall, and the leaked electromagnetic waves are received via the antenna 22 as described above. The leakage point 36 can be detected by receiving the data at the device 21. However, the electromagnetic wave of a certain frequency at a certain time may not form the above-described electric and magnetic field components at the leakage point 36,
At this point, electromagnetic waves are unlikely to leak. Therefore, assuming that electromagnetic waves of such a frequency are continuously excited, the leakage point 3 of the gas pipe 14 due to the leaking electromagnetic waves 3
Detection of 6 is difficult.

However, in the present invention, since the frequency of the electromagnetic wave excited in the gas pipe 14 changes with time, even if an electromagnetic field distribution which is difficult to leak from the leak point 36 at a certain frequency at a certain time, At different times at different frequencies, the electromagnetic field distribution changes, and the electromagnetic wave leaks from the leak point 36, so that the leak point 36 can be detected.

In the above embodiment, the excitation of the electromagnetic wave to the gas pipe 14 is performed by the excitation portion 12 attached to the opening 16 on the side of the tee 15.
It is also possible to perform it by an exciter which is cut and attached to No. 4.

Further, in the above-mentioned embodiments, the object of inspection is a gas pipe, but the present invention can be applied to an appropriate metal pipe in addition to the gas pipe.

[0015]

The present invention is as described above. Therefore, in an inspection method for detecting a leaked portion such as a corrosion hole formed in a gas pipe by using electromagnetic waves, a fixed electromagnetic field distribution is provided in the pipe. Since it is not formed, there is an effect that the leakage of the electromagnetic wave from the leakage point can be ensured, and thus the leakage point can be surely detected.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an overall configuration of an embodiment in which the method of the present invention is applied to detection of a leak point in a gas pipe.

FIG. 2 is an explanatory diagram showing an example of changes in frequency with time according to the present invention.

FIG. 3 is an explanatory diagram showing another example of changes in frequency with time according to the present invention.

FIG. 4 is a graph showing changes in frequency with time according to the present invention.
It is explanatory drawing which shows another example.

FIG. 5 is a cross-sectional view showing an example of an excitation unit in the present invention.

FIG. 6 is a schematic diagram showing an entire configuration of a conventional leak location detection of a gas pipe using electromagnetic waves.

[Explanation of symbols]

 1,11 Transmitter 2,12 Excitation part 3,13,23 Coaxial cable 4,14 Gas pipe 5,18 Probe 6,22 Antenna 7,21 Receiver 8,36 Leakage point 15 Tee 16 Opening 17 Lid 24 Support 25 lock nut 26a, 26b screw part 27 mounting hole 28 flange part 29 center lead 30 shield wire 31 clamp 32 washer 33 gasket 34 insulator 35a, 35b screw part

Claims (3)

[Claims] 1. A method for inspecting a leaked portion of a pipe by exciting the electromagnetic wave to a pipe to be inspected by a transmitting device to propagate the inside of the pipe and receiving a leaking electromagnetic wave by a receiving device. A method of inspecting a pipe by electromagnetic waves, characterized by changing with time 2. The method for inspecting a pipe by electromagnetic waves according to claim 1, wherein the frequency of the electromagnetic waves is continuously changed by sweeping. 3. The method of inspecting a pipe by electromagnetic waves according to claim 1, wherein the frequency of the electromagnetic waves is changed stepwise.